The present invention relates to a rotating tire laser mapping machine and, more particularly, to an alignment device for such a machine.
A laser mapping machine is used to measure the tread wear in a tire as it progresses, for example, through a standardized wear test. The machine can comprise a hub upon which the tire is mounted, a motor-driven shaft connected to the hub, a laser probe positioned to measure tread wear (i.e., the distance from the probe to the tire surface), a rail for moving the laser probe across the tread of the tire, and a microprocessor for translating the laser probe readings into tread depth data.
A standardized wear test typically comprises the steps of initially laser mapping the tire tread, running the tire through a series of wear exercises, laser mapping the tire tread after each set of wear exercises, and then comparing laser mapping data to determine the wear characteristics of the tire. Accordingly, in order for the comparisons to accurately reflect wear, intra-component alignments in the laser mapping machine must not change between laser mappings. In the past, this has been accomplished by measuring the horizontal distance between the rail and the shaft and by determining the perpendicularity of the hub to the shaft. Specifically, a calibration T-bar has been provided with a measuring surface to measure the rail-shaft distance and to measure the rail-hub distance at different shaft rotation points. (If this rail-hub distance is constant at different shaft rotations, the perpendicularity of the shaft to the hub is confirmed.) The T-bar further includes a calibrated gage block of a known height so that a measurement can be taken to verify laser calibration.
The inventors appreciated that the horizontal probe-shaft distance and the shaft-rim orientation provided by the prior art calibration T-bar are not sufficient to quantify all of the alignments critical to ensure consistent laser mapping. More particularly, the inventors appreciated that six alignment parameters need to be quantified to guarantee test integrity, specifically (1) the perpendicularity of the laser to the laser rail in the horizontal plane, (2) the perpendicularity of the laser to the laser rail in the vertical plane, (3) the parallelism of the laser rail to the shaft in the horizontal plane, (4) the parallelism of the laser rail to the shaft in the vertical plane, and (5) the perpendicularity of the hub to the shaft; and (6) the degree of radial run-out in the shaft.
The present invention provides an alignment device that can determine these six alignment parameters. The alignment device is designed to be mounted directly to the laser mapping machine (in place of the tire) and includes a plurality of surfaces from which laser measurements can be taken for alignment purposes. In other words, a laser mapping is taken of the alignment device and the measurement data derived from the alignment surfaces is used to determine alignment issues.
More particularly, the present invention provides an alignment device shaped and sized to be mounted on the hub of a laser mapping machine in place of the tire, and comprising alignment surfaces S1-S5. The mapping of the alignment surface S1 and the mapping of the alignment surface S2 reflect the perpendicularity of the laser relative to the rail in a first direction and a second direction perpendicular to the first direction. The mapping of the alignment surface S2 and the alignment surface S3 will reflect the parallelism of the rail to the shaft in the first and second directions. The mapping of the alignment surface S4 and the alignment surface S5 will reflect radial and out-of-plane wobble.
The present invention provides these and other features hereinafter fully described and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative embodiments of the invention. This embodiment is indicative, however, of but one of the various ways in which the principles of the invention can be employed.